Coded track circuit singaling system



April 14, 1953 i J D. HuGHsoN coDED TRACK CIRCUIT STGNALING SYSTEM Filed Feb. 13, 1946 8m" In l TV l 0W R mu @MFN OOGF. ZW N E nu @u M INVENTOR. BY

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Hl' A TTORNE Y Patented Apr. 14, 1953 CODED TRACK CIRCUIT SIGNALIN G SYST .l Donald Hughson, Rochester, N. Y., assignor to General Railway N` Y.

Signal Company, Rochester,

Application February 13, 1946, Serial No. 647,270

4 Claims. 1`

The present invention relates to automatic block signalling systems for railroads usingcoded track circuits, and more particularly pertains to an improved .form of coded track circuit for use insuchsignalling systems. i

Theconventional coded track circuit block signalling system provides for the application of current impulses at the exit endof each coded track circuit section with intervals between the successive pulses which have been conveniently termed off-periods. These time spaced impulses are transmitted at different distinctive code rates in each track section in accordance with the traino conditions in advance of that section, and comprise what are termed driven codes. At the entrance end of a conventional coded track circuit section, a code following track relay is connected aross the rails of that section to receive the driven code impulses and act upon suitable decoding apparatus which is distinctively governed in accordance with the particular rate of the driven code then being received. 'Ihis decoding apparatus acts to govern the indications of the associated signal in accordance with traic conditions in advance of that signal, and also acts to select the code rate to be applied to the'next track section in the rear. i

A block signalling system using such conventional coded track circuits encounters several practical dihculties in actual practice'. For vexample, it may happen that the presence oi a foreign Vcurrent in a track section will cause improper operation of the code following track relay. Such foreign current may be due to the leakage of current from some power line or may be due to the` electrolytic action occurring in the track circuit itself `because of the various chemical constituents in the ballast and the presence of a proper amount of moisture under varying Weather conditions. l

`The presence of a foreign current, regardless of its source or cause, in some cases entirely prevents the proper operation of the `track relay of a section in response to the application of `code pulses at the exit end of that section. In `other cases, the presence of foreign current together with the coded current causes the track relay to become so magnetically saturated as to render the relay slow in responding to the ofi-periods between successive impulses thus distorting the code pattern received. It will be readily appreciated that the duration of the oli-periods of a code should be approximately equal to theimpulse periodso-f that codedn order to .have a symmetricalfeffect upon: the decoding apparatus which 2 c is distinctively responsive to the different code rates. However, it should be understood that the particular time ratio selected as between the impulse and space periods is dependent upon the character of the decoding apparatus, but regardless of the particular ratio selected, it is essential to maintain the proper ratio of different track circuit conditions in order to givethe. optimum results. v

A further difficulty is encountered in coded track circuits due' to the 'wide variation in the ballast leakage of the track circuit. With high ballast resistance conditions i. e. when the ballast is dry, the track circuit maybe adjusted to give the proper amount of current at the track relay end so that the code following track relay will properly respond to the code pulses applied at the exit end. However, a change in weather conditions i, e. the presence of moisture in the ballast, causes the ballast resistance to decrease so as to draw current away from the code following track relay at the entrance end to the section. In such a case, even though the track relay receives suiiicient current to eiiect its operation, it is shunted by the low ballast resistance which renders it slow in its release time since the stored magnetic energy in the relay results in an inductive current which flows through the track relay and the ballast leakage resistance. This condition distorts the operation of the code following track relay with respect to the actual time spacing and duration of the pulses impressed on the track circuit. Fo-r example, if the coding pulses on the track circuit have substantially the same duration as the time spaces between pulses, the track relay with its slow release operation would distort the eiect of these impulses on the decori` ing apparatus. In other words, the contacts of the track relay would remain in one position for the pulse period longer than in the opposite position for the time space, so that the effect would not be uniform on the decoding apparatus. This distortio-n may be so severe as to cause failure of the decoding apparatus to properly respond.

On the other hand, the usual method of` adjusting coded track circuits is `to supply `sufficient energy to the track circuit to` cause operation of the track relay under the lowest resistance ballast conditions expected to occur, then as the ballast dries out and its resistance increases a considerable added amount of energy is supplied to the track relay. In some cases this will result in a suiiicient over-energization of the track relay as to substantially increase itsrelease time and distort the time ratio of the code pulses to the separating spaces. If the conditions are severe enough, it may happen that the track relay will not have sufcient time to release before the next successive code pulse is received. As above pointed out, any delay of the track relay in releasing at the end of a code pulse applied to the track circuit will have an adverse effect upon the decoding apparatus.

In view of the above and other conditions which may be encountered in practice, it is proposed g currents in the circuit as well as being so organ ized as to provide for the proper time response of the code following the track relay regardless of varying ballast conditions.

Generally speaking and without attempting to define the nature or scope of the present invention, it is proposed to accomplish the purposes of the `present invention by providingv acoded track circuit having a code followingftrack relay inductively coupledto the track circuit by a suitableztransformer and having improved means for applying code pulses tov the track circuit. It is proposed that the code followingtrack relay shall be` offthe two position stick` or stay-Where-put type, whereas the code applying apparatus is so organized as tov cooperate with the code receiving apparatus in a manner to materially reduce the amount of current that is required to be broken through the code transmitting contacts.

With this organization, the track relay is responsivevonly to the diiiferent current changes in the track-circuit i. e., when an impulse is applied or removed. The current'change in the primary vwinding of the transformer upon the applicationof a code impulse causes a current pulse to iowin one. direction through the track relay, vwhereas the termination'of such a code impulse causes a decreasein current vin the pri` mary winding of the transformer to thereby cause a current pulse .of the opposite polarity to flow through the trackrelay. In this way, .the track relayv is operated to its oppositepositions atthe beginning and endof each cod'eimpul-segapplied to the track circuit. Such an organization is practically immune to thepresenceof foreign direct current in the coded track circuit, and various. changes-in ballast conditions havegvery little efiectupon thetime of operationgof. the track relay.

I Thus, it will be readilyapparent that onenbject of thel present invention is to. providea. more sensitive and reliable code following track relay organizationfcr use in coded track. circuits which organization overcomes certain of .the ditculties encountered in actualpractice.

Other objects, purposes Y and characteristic features of the lpresent invention'will .be .in part obvious from the accompanying drawings and :in part pointedout as the description ofthev inven-` tion progresses.

In describing the invention in detail, reference will be made to the accompanying drawings, in which like referencecharacters designate corresponding parts throughout the. several views,- and in which:

Fig. 1 shows diagrammatically one formthe present invention maytak'e-in a coded track circuit by using a two-position magnetic stickftype relay inductively coupled to thetrackcircuit';

ligi- '2 Jshows diagrammatically another form the present invention -m-ay take by-the use. cfa

4 two-position mechanically held relay of the neu tral type inductively coupled to the track circuit;

Fig. 3 illustrates diagrammatically another form the present invention may take by the use of a neutral differential stick relay inductively coupled to the track circuit;

Fig.v Li-illustrates diagrammatically a modified code impulse applying organization; andvv Fig. 5 illustrates one specic form of transformer that may be employed for more advantageously accomplishing the objects of the present invention;

For the purpose of simplifying the illustration, and facilitating: in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatcally and certain conventional illustrations have been employed, the drawing having been made more with the purpose of making it easy to understand the purpose and mode of operation than with the idea of illustratingV the f specific construction .and arrangement of parts that .would be. employed in practice.

Thus, thevarious relays ,and their contactsV are illustrated in a conventional mannenand sym. bols are used toV indicate connections to the terminals of batteries or other-,suitable sources .of electric current instead of indicating all the-wire connections to these terminals-.Y` Thesymbols and-() are employed to indicatethe posi tive and negative terminals respectively ofsuitf able batteries or other sources of direct current, and the circuits with which these symbolsl are employed are assumed to always have current flowing in the same direction, although it is-to, be understood that .in some cases alternating. current may be substituted for the direct current if desired, and in such cases the and (--).sy,m, bols are to be considered as'indicating the` relative instantaneous polarities of the alternating current. In certain instances, batteries` andtheir associated connections are shown. indetail instead of using symbols so asto make the circuit organization more clear and definite.

With reference to Fig. 1. ofthe-accompanying drawing, av stretch oftrack hasbeenshown as divided into track sectionsby suitable vinsulated joints lofwhich thetracksection 2T hasbeen shown completely and track sections AIT and 3T.v in part only. The color light type signals 2 and-3 are shown at the entrance ends of the-track sec tions 2T and 3T respectively. These -signalsmay of course be of any otherv suitable type-desired.

At the exit end of the trackv section 2T., acode transmitting relay SCP-is provided with a contact which in aback contactingposition closes a circuit through wire 23 to shunt the track secs tion 2T, but in a front contactingposition conf nects the track battery t and resistor `'l in :series across the track section to apply a code pulseof energy. This Acode transmitting relayCP is controlled through front contact 8 of relay 3H so as to apply a codeof theV 18o pulse per minute type by reason of the v.operation of an associated coder contact I80C; while the closurecf back contact of relay 3H connects the relayCP `to the coder contact iC to effect theapplicationiofa-codefof the 75 code pulse perminute rate., This relayI-I is governed through atrackrelay TR-iinduc-l tively coupled to the track section 3T :by:v the transformer STF as more specioallydescribed in connection with theapparatus atthe entrance end to the track section 2T.

Referring to the left hand end. of the track section .z 2T. conveniently referred to as the ens trance `end of the track section. assuming east bound trailic to be `thenormal direction of train movement, it will be seen that the track `relay 2TR is inductivelycoupled through a transformer *ZTF to the track `rails of the track section 2T.

This transformer 2TF is an iron core transformer having primary winding 9 and a secondary winding I0. A

It should be understood that the transformer 2TF may be of any suitable construction of the `usual type as illustrated by the conventional transformer symbols. .Howeven in order to obtain the optimum results from the track circuit organization of the present invention,- it is preferableto have theprimary-secondary turn ratio properly selected to match the surge impedance of the track relay y2TH. with the-surge impedance of thetrack circuit when the track circuit is at its 'lowest` ballast resistance condition. This matching of the surge impedance under the most adverse conditions is desirable to obtain the proper operation of the track relay under such conditions since the maximum transfer of energy is effected when the impedances are thus matched. However, under other conditions i. e. when the ballast resistance increases, the supply of energy to the primary winding of the transformer 2'IFwill be greater so that even though theimpedances are not exactly matched, there will be a sumcient transfer of energy to the track relay ZTR t effect its operation.

It is also preferable that the transformers, such as transformer 2TF, should be of the open magnetic circuit type as illustrated in Fig. 5 rather than of the usual closed magnetic Vcircuit type.

However, it should be understood that Vsuch struc..

'tureis not required for the operation of the present invention; but.. since it improves the timing characteristics of the organization, it is considered to be a preferred form and will be discussed in greater detail, as the description progresses. l Y

Each track relay, such as track relay 2TR, is ofthe two-position magnetic stick type, that is, itis a relay of the polarized type having contacts which,4 are actuated to one position or the other depending upon the polarity of the energy applied to the relay, and these contacts remain in their last actuated positions until energy of the opposite polarity is applied. Such a magnetic stick type relay may take different forms, one such relay having been disclosedin the -.prior patent to Hailes et al.,Pat,ent No. 1,929,094 dated Octoberi3,:1933. However, the more rugged type of track relay is usually' desirable such as having the general structural characteristics disclosed inthe `Patent No. 2,360,664 granted October 17, 1944,A to O. S. Field. This Field patent structure is shown as being a polarized biased relay, `but such relay can be readily changed to a two-position magnetic stick type relay by merely removingA the biasing spring, and in this way the magnetismA provided by `the permanent magnets causes the armature to remain in its last operated position until therelay windings` are energized with an opposite polarity.

, The track relay 2TR is provided'with a contact II .which energizes the opposite `halves of a split 4primary Winding of a decoding transformer I 2.i The-secondary winding of this decoding transformer is alsoprovided with a mid-tap connected through the-winding of a home relay A2H tp `a rectifying contact I3 of the relay 2TR. Thus, as therelay ZTR` operates its contactsl I and I3 to their opposite positions, inductive pulses are caused tov flow., in 'thesame directionthrough the windings of the relay 2H. This causes the relay 2H to be picked up when the track relay 2TH, is operated atv either the code rate' or the 180 code rate.

The decoding transformer I2 is also provided with'secondary winding I4 which through condenser I5 supplies the primary winding of `a transformer` -16 withinductive pulses and this circuit is so tuned as to be responsive to the 180 code rate alone and when that code rate is supplying the secondary winding of the transformer I6 sucient energyis supplied through the rectifier unit I'I to effect the picking up of the relay 2D. In other words, the relay 2H is picked up during the reception of a code of either a 75 or 180 code rate, but the relay 2D is picked up only upon the reception of a code of the 180` code rate.

Since the response of the relay 2D is dependent upon a tuned circuit, and a tuned circuit responds more readily to one particular frequency, it can be readily seen that it is desirable to provide substantially equally spaced inductive pulses for the tuned circuit `during the reception of the 180 code rate.

WhenA the relays 2H and 2D are both picked up. front contacts 20 and 2| are closed to energize the green lamp G of the signal I2; but when the Vrelay 2D is deenergized, as will occur during the reception of a '75 code rate, the front contact 20 supplies energy through back contact 2l to energize the yellow lamp Yrofthe signal 2. The absence` of all code allows the relay 2H to release, as will occur during the presence of a train in the track section 2T, to close the back contact 20 and energize the red lamp R of the signal 2. It can thus be seen that the 1180 code rate in the track section 2T causes a green aspect to be displayedby the signal 2, while a 75 code rate in the track section 2T causes a yellow aspect to be displayed by the signal v2.

The presence of a 75 or 180 code rate in the track section 2T effects the picking up of the relay 2I-I to close front contact 22 and cause a 180 code to be applied to the track section IT in the rear, but when no code is being received, and the relay 2H is deenergized, back contact 22 is closed so as to apply a 75 code rate to the track section IT in the rear.

The different code rates are provided by coding contacts IBC and 15C whichmay be of any suitable type, that is, they may be motor driven or they may be code oscillators of the type disclosed, for example, in the prior Patent No. 2,351,588 granted to O. S. Field, June 20, 1944. The coding contacts I C and 15C are assumed to produce codepulses per minute and '75 code pulses per minute respectively, although it is `to be understood that different code rates may be employed if desired.

Regardless of the particular code rate being applied` to the track section 2T, which is of course typical .of all of the track sections of the block signalling system, the application of each impulse 'to the track rails of track section 2T causes a current ilow through the primary winding 9 of the transformer ZTF. During the rise in current through the primary winding, an impulse is cre-` ated in the secondary winding I0 in such a direction as to cause the contacts II and I3 ofthe relay 2'I'Et to be actuated to left-hand positions in Which they are held by the inherent polarized characteristics of the relay even though current flow through the track relay 2TR ceases. In other words,` while thecurrent impulse is rising to its 9 generally speaking the foreign current will have no practical effect upon the track circuit until such current is of such a high valueas to materially magnetize the core of the transformer ZTF.

Similarly, as above mentioned briefly, the low resistance of the ballast of the track circuit under certain weather conditions acts as a shunt across the conventional track relay so as to maintain self-induced current in the winding of the track relay thereby holding its armature picked up for an appreciable time after termination of an impulse. In the present organization, the termination of an impulse and a change in current flow through the primary winding will cause a momentary impulse in the secondary winding to actuate the contacts of the track relay to the proper position, and any prolongation of such inductive condition due to the low ballast resistance does not adversely act on the track relay. In other words,.the initial decay of current at the end of an impulse causes an immediate response of the track relay. Thus, very low resistance ballast conditions fail to produce the disadvantageous distortion of the code following track relay operationin the present invention, and this insures the proper response of the decoding apparatus to the different distinctive codes.

In some cases the foreign current will be due to some external source of energy, while in others it may be due to the electrolytic action occurring Within the track circuit ballast connecting .the two rails of the track circuit. In still other cases, it may happen that the vtrack circuit acts somewhat similar to astorage battery so that continued `application of code pulses will tendto build up a potential between the two rails of the track circuit. In such a case, the shunt 23 acts to dissipate the stored potential `in the track cir.

cuit between code pulses so as to prevent the accumulation of any substantial potentialacross the vtrack rails.

Regardless of the particular source of the foreign current in the track circuit, it is apparent thatthe shunt connection 23 will tend to dissi-4 pate any energy existing inthe track circuit during the off-periods of the code then being applied. Thus, insofar as the shunt 23 acts to cause a reduction in foreign potentials across the`track rails of the track circuit, it also causes amorevrapid decrease in the current flowing through the `primary winding 9 of the transformer 2TF. "Since upon the rate of change of current in the primary.

winding 9, it is apparentthat the shunt 23 contributes to the end of producing more substantial current pulses in the track relay to operate it to itsopposite positions. However, it is to be understood that the track circuit of the present invention will operate within certain ranges of values and constants of the track circuit and apparatus withoutthe shunt 23, which shunt 23 is provided for increasing the range of operation of the track circuit under certain conditions that may be encountered in practice.

.With reference to Fig. 2 of the accompanying drawings, it is noted that the transformer 2TF has its secondary winding l connected to a relay ZTR2 through a rectifier Rl and another rectifier R2. `This track relay 2TH2 has two windings 26' winding 21 is energized these contacts are actuv ated to right hand positions. when the contacts of this relay are operated to either position, they* remain in that position until operated to the op` posite position by reason of suitable mechanical means, such as a mechanical toggle arrangement, or the like. l

Whenever an impulse is applied to the track circuit and the resulting pulse induced in the secondary winding takes place, such induced pulse ows through the rectifier Rl to energize- For this reason the contacts i l2 and |32 are actuated to their opposite positionsalternately at a rate dependent upon the rate of thev code pulses applied to the track circuit, and these contacts of the invention contemplates a signalling system having coded track circuits such as shown .in Fig.`

1 but employing relays ofthe type disclos'edin1 Fig. 2 in place of the magnetic stick type relays disclosed in connection with Fig. 1. This form of the invention operates in the sameway as de-`v scribed in connection with Fig. 1, and. gives th same advantageousfeatures.

With reference to Fig. 3 of the accompanying drawings, it will be seen that a track relay` Z'IR is provided having two windings. -This relay 2TH.3 is a neutral type relayand its upper Winde ing is connected to the secondary winding iii' of the transformer ZTF'while its lower winding is connected through a stick contact 3B and re sistor 3i to a suitablgsource of energy. Its; contacts H3 and |33 are connected to decoding apparatus the same as shown in Fig. 1.' In. other words, this form .of the invention contemplatesv -a 'systern the same as disclosed in connection with Fig. l but -having a relay of the type shown` in Fig. 3 substituted for the magnetic stick typev relay ETR shown in Fig. 1. A

Upon theapplication of a code pulse torthe track circuit; a pulse is induced in the secondary. winding l0 of the transformer ZTF and this pulse iiows through the upper windingof `the trackA relay ZTI?.3 causing such relay to pick up. As soon as'front-V contact 30 `is closed a stick circuit is established lthrough the lower winding ZTRS; and since the directionof energy by such pulse in theupperwinding of the relay isthe same as' the direction `of energization by the stick circuit,` the relay remains picked up eventhough `the momentary pulse flowing through its upper wind#1 ing ceases. i l 'i Upon the termination of a code pulse in the track circuita pulse is induced in the secondarywindingr iil `of transformer 2TF which is in the-v opposite direction to the pulse induced atthebeginning of the code pulse of the track circuit. Such momentary energization of the track. relay 2TR3 in the reverse direction acts to neutralize induced in the secondary winding ill ofthe transformer. In this way the beginning ofa a code pulse in the track circuit causes the relay' 2ER3 fito. be jpicked up, Vwhile the ,termination ci such code ispulse `in the :track lcircuit vcauses the relay ,-YZTRS .to be -dropped away. This .form -of the ain-ventionis contemplated as;having-the same advantages and ...operations "pointed .out in ycon-- nection with Fig. 1 which need not berepeated indetail.

-Referring to :.Fig. 4 it ,isito be vnotedthat the code :applying apparatus -shown in :this -form Aof the invention imay besubstituted .for the code applying apparatusdisclosedzin Figjl. `Inother words, the-shunt Z3 of Fig. lmay b-ererrrovedv and havefsubstituted therefor a track battery Adconnectedtinfser-ieswi-th aaresistor l. .Each'ftime the code=transmitting relay .30124 .is pickedup .to-:close frontfcontact f 54 andapply 1a code pulse :fromfthe track rbattery 154,A energy is applied "to v,the track circuit `for actuating the code following track relayiat thesoppositeend of ,theltrack circuit to one position through its inductivecouplingas described :in .connection 'with either .of :the -iorms shown.in .Eig.l, 210123. "At theend;of,suchg code pulse, (the -code ktransmitting .relay .'3CP4 iis :released :andthe back icontact A5451s closedto .apply energy .to :the :track circuit from the -=battery alii! of fthe Yopposite polarity. This causes =a 4flow of current 'through lthe primary winding 9 of :the transformer 2TF1of Fig. 1, .2, or vI'Zzinrthereverse direction.

.theyreversal of current in the primary windingvgitends .to force'the freversalcfimagnetic ux zinitheftransformer core, itftends to cause a more rapid ux changeitofproducea fpulsefof increased amplitude .in .the .secondary :winding I'U. .Although this condition is present -`to some extent, its effectiveness :is Vsomewhat ,decreased ducato the'attenuatingreftect oi the track circuit upon 'code pulses.

The more :important feature :of this iorm of the invention resides .inithe fact 'that the :swing cfzthe rnagneticflux ofthe transformer from Athe peaksof :one polarityto the peaknf the opposite polarity'has 'an additive eect in'producng `a current .pulse for :operation of the track relay. Since-this is true, :itis apparent that thepeak ofsea'chipclarity need be only-.about'onehaliithe peak :value `requiredain Eig. y1 'where .only one polarity of current pulse Tis employed. This means that ithe ,energy -fapplied `4for .each code pulserbyzthe.contactalfoi Irelay 3GPAL will be about half "the v`energvvalue required for veach :pulse in Fig -l Thus, l,the front v and back .contacts .54 each have to carry andbreak less current-,and wilittherebyllast. longerrthan whenv the-organiza tion of Fig. L1 isemployed. .In .other words, .the

energycontrolled by-.front contact 5 -of ,Fig. 1 .is divided .between `,the iront and back points .of contact 5iL in Figi Since thenormalcurrent valuesare=reduced :by the addition of resistancev to-the resistors 14 and-AI, the Vsaine resistorsact to limit the current flow during the occupancy oftheztrackfcircuit by a train. This is a distinct advantage since ratherfheavy currents are-caused to-flow when: aftrackT circuit becomes Voccupiedby a ytrain and thebreaking of such :currents is very harm-ful -to the coding contacts.

V11n-brief, this formgof the inventipn contemplatedfbyFig. 4 includes the applicationof pulses (if-:opposite polarity applied .to kthe trackcircuit withoutany substantial intervening time fspaces .Y

between-the pulses to give an additive effect upon theinductively coupled track relay insuch a way asatopermitthe use of individual impulses of `reducedenergy levelsto thereby .reduce the wear on the code transmitting .contacts both .during normal vlcoding .operations v.and Vwhen .the trackl circuitris occupied-:by a train. Y

This `form 'of the -invention contemplated by Fig. el v,gives the same ,characteristic advantages provided hir-Fig. Vitin-.that it is immuneztdlimtted values cit-foreign current` sometimes encountered initrfackfcircuits. In .this connection, `it might-be notedthatthe reversal of polarity of the-code pulsesin the ytrack circuit :provides the r:same

.- total swingtfrom 'one peak value-fof vcurrentcinthe=transformer winding 9 -to the .peak value of currentHof-the opposite polarity regardless offthe presence-.of af-limited value of foreigncurrent oiv either polarity. 'In other'wordsthevparticular value fof foreign current present in th-e track circuit rat .any-fone 4time -and flowing `through :the

Winding'al merely'zfurnishesa 'different baseline on fthe :opposite r'sides ci` which lthe reversal foi codepulse `current :can swing. Because :of the 'total ,effect upon the track `relay remains-y the same `regardless of the'presence orzabsence of such 'foreign lcurrent values. f

It'will `thus V'beseenf'that a signalling system vhaving its Vdifferent track sections Aprovided with track-circuit apparatus organizedin accordance with -the-presentinvention willbe freeo'iwmany of the troublesomelconditions occurring 'inlthe conventicnal'coded'track circuits. Forthis reason,'it is believed'thatthe-present invention-is meritoriousandrepresents a decided advantage over priorcode'd track circuit systems.

Having described vseveral forms of a coded track circuitblock signalling system 'employing code transmitting and A'receiving apparatus crganized `in accordance with thepres'ent invenf tion to iobviate `difficulties in lconnection with foreign currents, and thelike, as embodyingthe present invention, it is desired'to be understood railroads :operable :in spite Vof .the presencewni4 stray ,foreign potentials :on the y.track rails, san insulated section of track, -code transmitting means vat/.one ,end'of Vsaid sect1on for applying.

sustained direct current code pulses at .different code 4'rates .in accordance with trafc conditions. said ,code transmitting rmeans Y causing said vcode pulses -to .have -leading and trailing edgesfsuccessiVely-.occurring at substantially equally spaced intervals,a code following track relayof the twoposition type associated with the opposite end of said section, circuit means .including'a--transformerlforfinductively coupling said relay toLthe rails of fsaidsect-ion,,saiditrackrelay beingfdistinctively responsive to y.the .polarity `of its :irn-` pulsef enengiaationrfrom said transformer :and ref fectivetofactuate :andhold its contacts .in 'Opposite ,positions alternately in response to the :successive impulses for the successive leading and trailing edges of :said sustained direct current code lpulses, and decoding means distinctively governedfby :theoperation ,of said trackgrelay lto its opposite positions at said different code rates for the control of wayside signals.

2. In a coded track circuit organization for railroads operable regardless of the possible presence of stray foreign potentials on the track rails, a section of track, code transmitting means at one end of said section for applying sustained direct current code pulses at different distinctive code rates in accordance with traflic conditions in advance, said code transmitting means causing said code pulses to have leading and trailing edges occurring in a continuous series at substantially equally spaced intervals, code receiving means at the other end of said track section including a transformer having primary and secondary windings mounted on a ferro-magnetic core with an air gap, said primary winding being connected across the rails of said track section, a polarized magnetic stick type relay connected across the secondary winding of said transformer, said relay having its contacts operated to one position by the current induced in said secondary winding for the leading edge of a code pulse and to the opposite position by the current induced in said secondary Winding for the trailing edge of a code pulse, and decoding means distinctively controlled in accordance with the operation of said relay at a rate corresponding to the rate of the direct current code pulses applied to the track rails.

3. In a coded track circuit organization for railroads operable regardless of the possible presence of stray foreign potentials on the track 'rails, a section of track, code transmitting means at one end of said section for applying sustained direct current code pulses at different distinctive code rates in accordance with traiiic conditions in advance, said code transmitting means causing said code pulses to have leading and trailing edges occurring in a continuous series at substantially equally spaced intervals, code receiving means at the other end of said track section including a transformer having primary and secondary windings mounted on the middle leg of an E-shaped ferro-magnetic core structure, said primary winding being connected across the rails of said track section, a polarized magnetic stick type relay connected to the secondary winding of said transformer, said relay having its contacts operated to one position by the current induced in said secondary winding for the leading edge of a code pulse and to the opposite position by the current induced in said secondary winding for the trailing edge of a code pulse, and decoding means distinctively controlled by the substantially uniform operation of said relay in response to the inductive pulses applied to it at a rate corresponding to the rate of the direct current code pulses applied to the track rails.

4. In a coded track circuit organization for railroads operable regardless of the possible presence of stray foreign steady potentials on the track rails, an insulated section of track, code transmitting means at one end of said section for applying sustained direct current code pulses at different distinctive code rates in accordance with traic' conditions, said code transmitting means causing said code pulses to have leading and trailing edges successively occurring at substantially equally spaced intervals, a code following track relay of the two-position mechanical staywhere-put type having separate windings for actuating its contacts to their opposite positions, circuit means including a transformer having its secondary windings connected through oppositely poled rectifier units to the windings of said relay and having its primary winding directly connected to the track rails of said section to cause said relay windings to be alternately energized successively for the respective leading and trailing edges of the direct current code pulses applied to said track section, and decoding means distinctively governed in accordance with the rate of the operation of said two-position track relay to its opposite positions alternately. I

J DONALD HUGHSON.

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